This invention relates in general to fluid actuators for causing movement of a piston relative to a cylinder. In particular, this invention relates to an intensifier type of fluid actuator using air and water as working fluids.
Fluid actuators are well known devices which are adapted to generate mechanical movement in response to the application of pressurized fluid, such as air or oil. A basic fluid actuator includes a hollow cylinder having a piston slidably disposed therein. The outer circumferential surface of the piston slidably and sealingly engages the inner circumferential surface of the cylinder so as to divide the interior of the cylinder into first and second chambers. When a pressurized fluid is supplied to the first chamber and the second chamber is vented, a pressure differential is created across the piston. This pressure differential causes the piston to slide relative to the cylinder in a first direction. Similarly, when a pressurized fluid is supplied to the second chamber and the first chamber is vented, the pressure differential created across the piston causes it to slide relative to the cylinder in a second direction. One or more fluid valves are usually provided to control the supply of pressurized fluid to and the venting of the two chambers of the cylinder so as to effect movement of the piston in a desired manner.
Typically, a rod is connected to the piston for movement therewith. The rod extends outwardly from the cylinder into engagement with a workpiece. Thus, when the piston is moved within the cylinder as described above, the workpiece is moved therewith. The magnitude of the force which is generated against the workpiece is equal to the product of the pressure of the fluid in the chamber and the surface area of the piston exposed to that pressurized fluid. Thus, for example, if the magnitude of the pressurized fluid is one hundred pounds per square inch (p.s.i.) and the surface area of the piston is two square inches, then the magnitude of the force exerted by the piston against the workpiece will be two hundred pounds. Fluid actuators of this general type are commonly used in a variety of applications.
In some applications, however, the magnitude of the pressurized fluid available for use by the fluid actuator is limited. For example, in a typical manufacturing facility, pressurized air may be generated by a central supply system at a standard pressure, such as one hundred p.s.i., for the entire facility. At the same time, the magnitude of the force necessary for the fluid actuator to perform a given task may be relatively large, such as one thousand pounds. If a basic fluid actuator structure as described above were to be used to perform this task, the piston would have to very large (ten square inches in this example) in order to generate the necessary force. Obviously, it is undesirable from several standpoints to provide such a physically large piston.
To address the problem of generating relatively large forces using limited fluid pressures and relatively small pistons, it is known to modify the basic fluid actuator structure to generate an increased amount of force. These modified fluid actuator structures, which are commonly referred to as intensifiers, use multiple interacting pistons to multiply the forces produced by the pressurized fluid against the pistons, while maintaining relatively small sizes for the pistons. A typical intensifier structure includes a cylinder which is divided by an internal manifold into two working areas. In the first working area, a first piston is provided which divides the interior thereof into first and second chambers. A rod extends from the first piston through the manifold into the second working area. In the second working area, a second piston is provided which divides the interior thereof into first and second chambers.
When pressurized fluid is supplied to the first chamber of the first working area, a first force is generated against the first piston as described above. Movement of the first piston causes corresponding movement of the first rod in the first chamber of the second working area. The first chamber of the second working area is filled with oil which is a relatively incompressible liquid. Thus, a second force is generated against the second piston because of the movement of the rod. The rod has a much smaller surface area than the first piston. Thus, the magnitude of the pressure generated in the first chamber of the second area against the second piston is multiplied relative to the original pressure exerted against the first piston. This multiplied pressure is applied against the surface area of the second piston and generates a multiplied force. A second rod connected to the second piston transmits the multiplied force to a workpiece.
The pressurized fluid that is supplied to the first chamber of the first working area is usually a gaseous fluid, with ambient air being the most common used gaseous fluid. Traditionally, a lubricating oil has been used for the non-compressible fluid in the other working chambers of the intensifier. The use of oil as such a working fluid has the advantage of lubricating various elastomeric seals that are disposed about the movable pistons and the inner walls of the various structures defining the chambers for proper sealing therebetween. In such known intensifiers, one or more helical grooves have been formed in the inner walls to trap oil therein to lubricate the seals as they travel over the grooves. The grooves are formed having such a depth as to trap a sufficient amount of oil therein to enable lubrication, yet small enough not to allow significant leaks around the seals between adjacent chambers. For example, it is known to form such grooves having a depth in the range of from about ten microns to about fifteen microns for sufficient use with oil. The use of oil as a working fluid also helps protect against corrosion for the internal metallic structures of the intensifier. Thus, the intensifier can be made with relatively inexpensive metal, such as conventional steel alloys, which may be susceptible to corrosion absent the presence of oil.
However, the use of known air/oil intensifiers in certain applications, such as in food preparation or medical equipment applications, has not met with great success. This is apparently the result of fear of contamination of the products being manipulating resulting from the leakage of the oil from the intensifier. Although the occurrences of such leaks are very rare, the use of known air/oil intensifiers in these and other applications have met with resistance from customers. The use of external shields and other devices are expensive, bulky, and generally difficult to use. Thus, it would be desirable to provide an improved structure for an intensifier that avoids the use of oil as a working fluid.
This invention relates to an intensifier type of fluid actuator using air and water as working fluids therein. The intensifier includes first and second bodies that can be separate components or incorporated into a single structure. The first body includes a first manifold connected by a first tube to a second manifold to define an intensifier chamber, a third manifold connected by a second tube to the second manifold to define a reservoir chamber, and a fourth manifold connected by a third tube to the third manifold to define a work chamber. An intensifier piston is disposed within the intensifier chamber and has an outer surface in sealing and sliding engagement with the first tube. The intensifier rod is secured to the intensifier piston and extends through the second manifold into the reservoir chamber. The intensifier rod is movable through the third manifold into the work chamber. A reservoir piston is disposed within the reservoir chamber and has an outer surface in sealing and sliding engagement with the second tube. The reservoir piston includes an opening formed therethrough. The intensifier rod extends through the opening formed in the reservoir piston. The reservoir piston separates the reservoir chamber to define a water reservoir chamber and an air reservoir chamber in selective communication with a source of air. The second body includes a fifth manifold connected by a fourth tube to a sixth manifold to define a piston chamber. A work piston is disposed within the piston chamber and has an outer surface in sealing and sliding engagement with the fourth tube. A work rod is secured to the work piston and extends through the sixth manifold from the second body. A plurality of ports are provided for selectively providing pressurized fluid in the intensifier chamber, the reservoir chamber, the first work chamber, and the piston chamber to selectively extend the work rod into engagement with the workpiece. Water is used as the working fluid in the fluid reservoir chamber and the work chamber to eliminate any contamination issues if any leaks occur.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.